Capacitively coupled compound loop antenna

ABSTRACT

A compound loop antenna (CPL) is described that includes a capacitively fed magnetic loop and/or a capacitively fed electric field radiator. Embodiments include single-band CPL antennas and multi-band CPL antennas. The CPL antennas have been reduced in physical size by capacitively feeding the loop and/or radiator. The embodiments include at least one e-field radiation element that is capacitively coupled or not capacitively coupled, at least one magnetic loop element that is capacitively coupled. A continuation of the magnetic loop may be continued with either a wire or a connection to a second layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit under 35 U.S.C. §119(e) of U.S.Provisional Application No. 61/556,145, filed Nov. 4, 2011, the contentsof which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

Embodiments relate to compound loop antennas (CPL) and particularly toCPL antennas that include a capacitively fed magnetic loop and/or acapacitively fed electric field radiator and/or a direct fed electricfield radiator.

BACKGROUND

The ever decreasing size of modern telecommunication devices creates aneed for improved antenna designs. Known antennas in devices such asmobile/cellular telephones provide one of the major limitations inperformance and are almost always a compromise in one way or another.

In particular, the efficiency of the antenna can have a major impact onthe performance of the device. A more efficient antenna will radiate ahigher proportion of the energy fed to it from a transmitter. Likewise,due to the inherent reciprocity of antennas, a more efficient antennawill convert more of a received signal into electrical energy forprocessing by the receiver.

In order to ensure maximum transfer of energy (in both transmit andreceive modes) between a transceiver (a device that operates as both atransmitter and receiver) and an antenna, the impedance of both shouldmatch each other in magnitude. Any mismatch between the two will resultin sub-optimal performance with, in the transmit case, energy beingreflected back from the antenna into the transmitter. When operating asa receiver, the sub-optimal performance of the antenna results in lowerreceived power than would otherwise be possible.

Existing simple loop antennas are typically current fed devices, whichproduce primarily a magnetic (H) field. As such they are not typicallysuitable as transmitters. This is especially true of small loop antennas(i.e. those smaller than, or having a diameter less than, onewavelength). In contrast, voltage fed antennas, such as dipoles, produceboth electric (E) fields and H fields and can be used in both transmitand receive modes.

The amount of energy received by, or transmitted from, a loop antennais, in part, determined by its area. Typically, each time the area ofthe loop is halved, the amount of energy which may bereceived/transmitted is reduced by approximately 3 dB depending onapplication parameters, such as initial size, frequency, etc. Thisphysical constraint tends to mean that very small loop antennas cannotbe used in practice.

Compound antennas are those in which both the transverse magnetic (TM)and transverse electric (TE) modes are excited in order to achievehigher performance benefits such as higher bandwidth (lower Q), greaterradiation intensity/power/gain, and greater efficiency.

In the late 1940s, Wheeler and Chu were the first to examine theproperties of electrically small (ELS) antennas. Through their work,several numerical formulas were created to describe the limitations ofantennas as they decrease in physical size. One of the limitations ofELS antennas mentioned by Wheeler and Chu, which is of particularimportance, is that they have large radiation quality factors, Q, inthat they store, on time average more energy than they radiate.According to Wheeler and Chu, ELS antennas have high radiation Q, whichresults in the smallest resistive loss in the antenna or matchingnetwork and leads to very low radiation efficiencies, typically between1-50%. As a result, since the 1940's, it has generally been accepted bythe science world that ELS antennas have narrow bandwidths and poorradiation efficiencies. Many of the modern day achievements in wirelesscommunications systems utilizing ELS antennas have come about fromrigorous experimentation and optimization of modulation schemes and onair protocols, but the ELS antennas utilized commercially today stillreflect the narrow bandwidth, low efficiency attributes that Wheeler andChu first established.

In the early 1990s, Dale M. Grimes and Craig A. Grimes claimed to havemathematically found certain combinations of TM and TE modes operatingtogether in ELS antennas that exceed the low radiation Q limitestablished by Wheeler and Chu's theory. Grimes and Grimes describetheir work in a journal entitled “Bandwidth and Q of Antennas RadiatingTE and TM Modes,” published in the IEEE Transactions on ElectromagneticCompatibility in May 1995. These claims sparked much debate and led tothe term “compound field antenna” in which both TM and TE modes areexcited, as opposed to a “simple field antenna” where either the TM orTE mode is excited alone. The benefits of compound field antennas havebeen mathematically proven by several well respected RF expertsincluding a group hired by the U.S. Naval Air Warfare Center WeaponsDivision in which they concluded evidence of radiation Q lower than theWheeler-Chu limit, increased radiation intensity, directivity (gain),radiated power, and radiated efficiency (P. L. Overfelt, D. R. Bowling,D. J. White, “Colocated Magnetic Loop, Electric Dipole Array Antenna(Preliminary Results),” Interim rept., September 1994).

Compound field antennas have proven to be complex and difficult tophysically implement, due to the unwanted effects of element couplingand the related difficulty in designing a low loss passive network tocombine the electric and magnetic radiators.

There are a number of examples of two dimensional, non-compoundantennas, which generally consist of printed strips of metal on acircuit board. However, these antennas are voltage fed. An example ofone such antenna is the planar inverted F antenna (PIFA). The majorityof similar antenna designs also primarily consist of quarter wavelength(or some multiple of a quarter wavelength), voltage fed, dipoleantennas.

Planar antennas are also known in the art. For example, U.S. Pat. No.5,061,938, issued to Zahn et al., requires an expensive Teflonsubstrate, or a similar material, for the antenna to operate. U.S. Pat.No. 5,376,942, issued to Shiga, teaches a planar antenna that canreceive, but does not transmit, microwave signals. The Shiga antennafurther requires an expensive semiconductor substrate. U.S. Pat. No.6,677,901, issued to Nalbandian, is concerned with a planar antenna thatrequires a substrate having a permittivity to permeability ratio of 1:1to 1:3 and which is only capable of operating in the HF and VHFfrequency ranges (3 to 30 MHz and 30 to 300 MHz). While it is known toprint some lower frequency devices on an inexpensive glass reinforcedepoxy laminate sheet, such as FR-4, which is commonly used for ordinaryprinted circuit boards, the dielectric losses in FR-4 are considered tobe too high and the dielectric constant not sufficiently tightlycontrolled for such substrates to be used at microwave frequencies. Forthese reasons, an alumina substrate is more commonly used. In addition,none of these planar antennas are compound loop antennas.

The basis for the increased performance of compound field antennas, interms of bandwidth, efficiency, gain, and radiation intensity, derivesfrom the effects of energy stored in the near field of an antenna. In RFantenna design, it is desirable to transfer as much of the energypresented to the antenna into radiated power as possible. The energystored in the antenna's near field has historically been referred to asreactive power and serves to limit the amount of power that can beradiated. When discussing complex power, there exists a real andimaginary (often referred to as a “reactive”) portion. Real power leavesthe source and never returns, whereas the imaginary or reactive powertends to oscillate about a fixed position (within a half wavelength) ofthe source and interacts with the source, thereby affecting theantenna's operation. The presence of real power from multiple sources isdirectly additive, whereas multiple sources of imaginary power can beadditive or subtractive (canceling). The benefit of a compound antennais that it is driven by both TM (electric dipole) and TE (magneticdipole) sources which allows engineers to create designs utilizingreactive power cancelation that was previously not available in simplefield antennas, thereby improving the real power transmission propertiesof the antenna.

In order to be able to cancel reactive power in a compound antenna, itis necessary for the electric field and the magnetic field to operateorthogonal to each other. While numerous arrangements of the electricfield radiator(s), necessary for emitting the electric field, and themagnetic loop, necessary for generating the magnetic field, have beenproposed, all such designs have invariably settled upon athree-dimensional antenna. For example, U.S. Pat. No. 7,215,292, issuedto McLean, requires a pair of magnetic loops in parallel planes with anelectric dipole on a third parallel plane situated between the pair ofmagnetic loops. U.S. Pat. No. 6,437,750, issued to Grimes et al.,requires two pairs of magnetic loops and electric dipoles to bephysically arranged orthogonally to one another. U.S. Patent ApplicationUS2007/0080878, filed by McLean, teaches an arrangement where themagnetic dipole and the electric dipole are also in orthogonal planes.

Commonly owned U.S. Pat. No. 8,144,065 teaches a linear polarized,multi-layered planar compound loop antenna. Commonly owned U.S. patentapplication Ser. No. 12/878,018 teaches a linear polarized, single-sidedcompound loop antenna. Finally, commonly owned U.S. Pat. No. 8,164,528teaches a linear polarized, self-contained compound loop antenna. Thesecommonly owned patents and applications differ from prior antennas inthat they are compound loop antennas having one or more magnetic loopsand one or more electric field radiators physically arranged in twodimensions, rather than requiring three-dimensional arrangements of themagnetic loops and the electric field radiators as in the antennadesigns by McLean and Grimes et al.

SUMMARY

Embodiments described herein are comprised of a CPL antenna thatincludes a capacitively fed magnetic loop and/or a capacitively fedelectric field radiator. Embodiments include single-band CPL antennasand multi-band CPL antennas. The CPL antennas have been reduced inphysical size by capacitively feeding the loop and/or radiator. Theembodiments include at least one e-field radiation element that iscapacitively coupled or not capacitively coupled, at least one magneticloop element that is capacitively coupled. Acontinuation of the magneticloop may be continued with either a wire (3D) or a connection to asecond layer (2D).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a front of an embodiment of an antenna with acapacitively fed magnetic loop and a capacitively fed electric fieldradiator.

FIG. 2 illustrates a back view of the embodiment of FIG. 1.

FIG. 3 illustrates a perspective view of the embodiment of FIGS. 1 and2.

FIG. 4 illustrates an embodiment of an antenna with a feed point andground connection.

FIG. 5 illustrates a front view of an embodiment of a 2.4/5.8 GHzmulti-band CPL antenna.

FIG. 6 illustrates a back view of the embodiment of FIG. 5.

FIG. 7 illustrates a perspective view of the embodiment of FIGS. 5 and6.

FIG. 8 illustrates a return loss diagram for the 2.4/5.8 GHz bands ofthe embodiment illustrated in FIGS. 5-7.

FIG. 9 illustrates a front view of an embodiment of a 2.4/5.8 GHzmulti-band antenna.

FIG. 10 illustrates a back view of the embodiment of FIG. 9.

FIG. 11 illustrates a perspective view of the embodiment of FIGS. 9 and10.

FIGS. 12-14 illustrate a front view, a back view and a perspective view,respectively, of an embodiment a multiband CPL antenna with acapacitively coupled magnetic loop.

FIG. 15 illustrates the feed point and ground connection of theembodiment of FIG. 12-14 when connected to a load

FIG. 16 illustrates a return loss diagram for the embodiment illustratedin FIGS. 12-15.

FIGS. 17, 18 and 19 illustrate a front view, a back view and aperspective view, respectively, of an embodiment of a multiband CPLantenna with a capacitively coupled magnetic loop and a cut loop wirecompleting the loop.

FIG. 20 illustrates a return loss diagram for the embodiment illustratedin FIGS. 17-19.

FIGS. 21, 22 and 23 illustrate a front view, a back view and aperspective view, respectively, of an embodiment of a double-sidedmultiband CPL antenna with a capacitively coupled magnetic loop with theloop completed on a second layer.

FIG. 24 illustrates a return loss diagram for the embodiment illustratedin FIGS. 21-23.

FIG. 25 illustrates further details of the embodiment illustrated inFIG. 23.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Compound loop antennas are capable of operating in both transmit andreceive modes, thereby enabling greater performance than known loopantennas. The two primary components of a compound loop (CPL) antennaare a magnetic loop that generates a magnetic field (H field) and anelectric field radiator that emits an electric field (E field). The Hfield and the E field must be orthogonal to each other to enable theelectromagnetic waves emitted by the antenna to effectively propagatethrough space. To achieve this effect, the electric field radiator ispositioned at the approximate 90 degree electrical position or theapproximate 270 degree electrical position along the magnetic loop. Theorthogonality of the H field and the E field can also be achieved bypositioning the electric field radiator at a point along the magneticloop where current flowing through the magnetic loop is at a reflectiveminimum. The point along the magnetic loop of a CPL antenna wherecurrent is at a reflective minimum depends on the geometry of themagnetic loop. For example, the point where current is at a reflectiveminimum may be initially identified as a first area of the magneticloop. After adding or removing metal to the magnetic loop to achieveimpedance matching, the point where current is at a reflective minimummay change from the first area to a second area.

Embodiments described herein are comprised of a CPL antenna thatincludes a capacitively fed magnetic loop and/or a capacitively fedelectric field radiator. Embodiments described herein will be describedin reference to single-band 2.4 GHz CPL antennas and 2.4/5.8 GHzmulti-band CPL antennas. However, it is to be understood that theprinciples described herein can be applied to create single-band andmulti-band antennas at other frequency bands. These CPL antennas havebeen reduced in physical size by capacitively feeding the loop and/orradiator. The basic properties of embodiments of such antennas are thatat least one e-field radiation element is capacitively coupled or notcapacitively coupled, at least one magnetic loop element is capacitivelycoupled, and the antenna maintains high efficiency. In addition, thecontinuation of the magnetic loop can be continued with either a wire(3D) or a connection to a second layer (2D).

FIG. 1 illustrates an embodiment of a 2.4 GHz antenna with acapacitively fed magnetic loop and a capacitively fed electric fieldradiator. FIG. 1 illustrates a front view of the antenna, FIG. 2illustrates a back view of the antenna, and FIG. 3 illustrates aperspective view of the antenna. Element C, may be approximately 0.25millimeters, is a capacitive gap that results in the lower left portionof the magnetic loop capacitively feeding the rest of the magnetic loop.The smaller the dimension of the capacitive gap, the lower the resultingfrequency of the magnetic loop. If the capacitive gap is too large, thecapacitive coupling begins to fail and the resonance of the antennadisappears. The position of the capacitive gap C, by moving itvertically along the left side of the magnetic loop, affects theimpedance matching. Thus, moving the capacitive gap C up and down may beused to tune the antenna impedance.

Element D, also being approximately 0.25 mm, is a capacitive gap for theelectric field radiator. As illustrated in FIGS. 1-3, the electric fieldradiator is the larger rectangular element 10 inside of the magneticloop and to the right of the capacitive gap D. To the left of thecapacitive gap D is a substantially rectangular shaped radiator feed 12.The radiator feed may be coupled to the magnetic loop via a traceelement 14. The electric field radiator may be coupled to the magneticloop via a trace F on the back plane of the antenna, as illustrated andfurther described in reference to FIG. 2. The capacitive gap D for theelectric field radiator may not be too large, otherwise the capacitivecoupling of the electric field radiator begins to fail and the resonancedisappears. The position of the capacitive gap D for the electric fieldradiator also affects the impedance matching, and it can be movedhorizontally (left and right) to tune the antenna impedance.

The cut on the magnetic loop that forms the capacitive gap C may resultin a monopole resonance being created on the lower left portion of themagnetic loop, indicated by element G. The monopole resonance may betuned by adjusting the location of capacitive gap C and by adjusting thelength of the monopole resonance element G. The monopole resonance G mayalso be tuned to turn the antenna design into a multi-band antenna.

Element E, referring to the right side of the magnetic loop, may be madethinner (inductive reactance) than the rest of the magnetic loop inorder to match the capacitive reactance in the capacitive gap C. WhileFIG. 1 illustrates an antenna with a capacitive gap C and a wide portionof the magnetic loop on the left side of the magnetic loop, embodimentsmay consist of antennas with the capacitive gap C and the wide portionof the magnetic loop on the right side of the magnetic loop, and withthe thinner portion E of the magnetic loop being on the left side of themagnetic loop.

The inductance and capacitance of the magnetic loop may be tuned byadjusting the width of various portions of the magnetic loop. Forinstance, the width of the top portion of the magnetic loop may beincreased or decreased in order to tune its inductance and reactance.Changes to the geometry of the magnetic loop may also be made to tunethe antenna performance. For example, the corners of the substantiallyrectangular magnetic loop may be cut at an angle, such as a 45 degreeangle.

FIG. 2 illustrates a back view of the antenna from FIG. 1. As noted,element F indicates a trace on the bottom layer of the antenna,connecting the electric field radiator to the magnetic loop. The tracemay also be placed on the top layer to make a single layer antennadesign. The perspective view from FIG. 3 shows that the trace F may bepositioned on a bottom layer, and that the trace F may connect directlythe magnetic loop to the capacitively coupled electric field radiator.

FIG. 4 illustrates the antenna with feed point A and ground connectionB. While the embodiments described herein show the antenna having a feedpoint on the left endpoint of the magnetic loop and a ground connectionon the right endpoint of the magnetic loop, alternative embodiments mayinclude an antenna having the feed point on the right endpoint of themagnetic loop and a ground connection on the left endpoint of themagnetic loop.

Embodiments of the 2.4 GHz antenna in FIGS. 1-4 include a capacitivelyfed magnetic loop and a capacitively fed electric field radiator.However, the electric field radiator need not be capacitively fed.Instead, embodiments can consist of an electric field radiator that isnot capacitively fed, but which may either be directly coupled to themagnetic loop or coupled to the magnetic loop via a trace. The antennacan also include more than one electric field radiator inside of themagnetic loop. When including more than one electric field radiator, afirst electric field radiator may be capacitively fed while a secondelectric field radiator is not capacitively fed. Alternatively, all ofthe radiators may be capacitively fed, directly coupled to the magneticloop, coupled to the magnetic loop via a trace, or any combination ofthese.

Compared to simple loop antennas, embodiments described herein have theadvantage of being antenna designs that are compound field antennas,easy to tune, fill in nulls in the radiation pattern from the magneticloop, increase efficiency, increase bandwidth, and are small in physicalsize. Compared to monopoles, embodiments described herein may have theadvantage of being antenna designs that are compound field antennas,stable, increased efficiency, and increased bandwidth.

The electric field radiator may be thought of as a shorted magnetic loopwith a trace connected to a first segment and a second segment (radiatorfeed) separated by a capacitively coupled gap, with the second segmentand the magnetic loop connected via return on the back plane of theantenna (or via the first and second segment). The return increases theelectrical length of the radiator.

At the 2.4 GHz frequency, the capacitively fed electric field radiatorand the capacitively coupled magnetic loop radiate in phase with eachother. Specifically, the electric field radiator and the portions of themagnetic loop adjacent to the capacitive gap C radiate in phase witheach other at 2.4 GHz. A farfield plot of the 2.4 GHz band for theantenna illustrated on FIGS. 1-4 indicates that the farfield pattern ofthe antenna is omnidirectional, similar to a dipole pattern.

In an embodiment, a compound loop antenna may comprise a magnetic looplocated on a first plane and generating a magnetic field, the magneticloop including a downstream portion and an upstream portion, thedownstream portion separated from the upstream portion by a capacitivegap that capacitively feeds the downstream portion of the magnetic loop,wherein the magnetic loop has a first inductive reactance adding to atotal inductive reactance of the antenna, wherein the capacitive gapadds a first capacitive reactance to a total capacitive reactance of theantenna. The compound loop antenna may further comprise an electricfield radiator located on the first plane, the electric field radiatorcoupled to the magnetic loop and configured to emit an electric fieldorthogonal to the magnetic field, wherein the electric field radiatorhas a second capacitive reactance adding to the total capacitivereactance, wherein a physical arrangement between the electric fieldradiator and the magnetic loop results in a third capacitive reactanceadding to the total capacitive reactance, and wherein the totalinductive reactance substantially matches the total capacitivereactance.

In the embodiment, the antenna may further comprise a radiator feedcoupled to the magnetic loop, wherein the electric field radiator ispositioned adjacent to the radiator feed, wherein the electric fieldradiator is separated from the radiator feed by a second capacitive gapthat capacitively feeds the electric field radiator, wherein the secondcapacitive gap has a fourth capacitive reactance adding to the totalcapacitive reactance. In the embodiment, the antenna may furthercomprise an electrical trace coupling the radiator feed to the magneticloop. In the embodiment, the electrical trace may couple the radiatorfeed to the magnetic loop at a connection point, the connection pointincluding an electrical degree location approximately 90 degrees orapproximately 270 degrees from a drive point of the magnetic loop, or areflective minimum point where a current flowing through the magneticloop is at a reflective minimum. In the embodiment, the radiator feedmay be directly coupled to the magnetic loop.

In the embodiment, the antenna may further comprise an electrical tracecoupling the electric field radiator to the magnetic loop. In theembodiment, the electrical trace may couple the electric field radiatorto the magnetic loop at a connection point, the connection pointincluding an electrical degree location approximately 90 degrees orapproximately 270 degrees from a drive point of the magnetic loop, or areflective minimum point where a current flowing through the magneticloop is at a reflective minimum. In the embodiment, the electrical tracemay be positioned on a second plane below the first plane.

In the embodiment, the electric field radiator may be directly coupledto the magnetic loop at a connection point, the connection pointincluding an electrical degree location approximately 90 degrees orapproximately 270 degrees from a drive point of the magnetic loop, and areflective minimum point where a current flowing through the magneticloop is at a reflective minimum. In the embodiment, a first width of afirst portion of the magnetic loop may be greater than or less than asecond width of a second portion of the magnetic loop. In theembodiment, adjusting a position of the capacitive gap along themagnetic loop may tune an impedance of the antenna.

An embodiment may be directed to compound loop antennas that produce atleast dual-band resonances. Embodiments herein may be described in termsof a 2.4/5.8 GHz antenna that covers the WiFi frequencies. Embodimentsmay also be used in Multiple Input Multiple Output (MIMO) applications.At least three configurations will be described: (1) a firstconfiguration consisting of a CPL antenna with a magnetic loop and acapacitively fed electric field radiator inside of the magnetic loop,(2) a second configuration consisting of a CPL antenna with a magneticloop and a capacitively fed electric field radiator outside of themagnetic loop; and (3) a third configuration consisting of a CPL antennawith a capacitively fed magnetic loop that generates a first e-field anda connected electric field radiator inside the magnetic loop thatcombines with the magnetic loop to generate a second e-field.

FIG. 5 illustrates a front view of an embodiment of a 2.4/5.8 GHzmulti-band CPL antenna. FIG. 6 illustrates a back view of the antennaand FIG. 7 illustrates a perspective view of the antenna. The antennaincludes a capacitively fed electric field radiator located inside of acontinuous magnetic loop. The electric field radiator is the largerrectangular element located on the inside of the magnetic loop, and theradiator feed is the smaller rectangular element located on the insideof the magnetic loop. The radiator feed is coupled to the magnetic loopvia a trace. The electric field radiator is separated from the radiatorfeed by a capacitive gap that capacitively feeds the electric fieldradiator. The electric field radiator is coupled to the magnetic loopvia a trace on the back side of the antenna as illustrated in FIG. 6.The electric field radiator covers the 2.4 GHz band, as illustrated bythe dotted line 16, and the lower right portion of the magnetic loopcovers the 5.8 GHz band, as illustrated by the dashed line 18.Specifically, the lower right portion and the right side of the magneticloop are the radiating elements for the 5.8 GHz band.

As illustrated in FIG. 6, an inductive trace 20 on the back side of theantenna connects the capacitively fed electric field radiator to themagnetic loop. The inductance of the inductive trace compensates for thecapacitance caused by the capacitive gap between the electric fieldradiator and the radiator feed. The capacitive gap acts as a path forthe current to flow to ground. In embodiments, the inductive trace onthe back side of the antenna may also be placed on the front side of theantenna. Finally, while the antenna illustrated in FIGS. 5-7 includes acontinuous loop, embodiments of the multi-band antenna may consist ofantennas with a capacitively fed magnetic loop.

FIG. 8 illustrates a return loss diagram for the 2.4/5.8 GHz bands ofthe embodiment illustrated in FIG. 5-7. The diagram shows that returnloss is minimized at approximately the 2.5 GHz band and at the 5.3512GHz band, but operational within the desired bands of 2.4 and 5.8 GHz.

FIG. 9 illustrates a front view of an embodiment of a 2.4/5.8 GHzmulti-band antenna, where the capacitively fed electric field radiator22 is positioned outside of the magnetic loop 24. The electric fieldradiator covers the 2.4 GHz band, as illustrated by the dotted line 26,while the lower right portion of the magnetic loop and the radiator feedcover the 5.8 GHz band, as illustrated by the dashed line 28. FIG. 10illustrates a back view of the embodiment of FIG. 9, illustrating thereturn trace 30. FIG. 11 illustrates a perspective view of theembodiment of FIGS. 9 and 10.

In an embodiment, a multi-band compound loop antenna may comprise: amagnetic loop located on a first plane and generating a magnetic field,wherein the magnetic loop has a first inductive reactance adding to atotal inductive reactance of the antenna, wherein a first portion of themagnetic loop is configured to emit a first electric field orthogonal tothe magnetic field at a first frequency band; a radiator feed located onthe first plane and coupled to the magnetic loop via a first electricaltrace, wherein the radiator feed is configured to resonate in phase withthe first portion of the magnetic loop at the first frequency band; andan electric field radiator located on the first plane, the electricfield radiator coupled to the magnetic loop via a second electricaltrace positioned on a second plane below the first plane, the electricfield radiator positioned adjacent to the radiator feed and separatedfrom the radiator feed by a capacitive gap, wherein the electric fieldradiator is configured to emit a second electric field at a secondfrequency band and orthogonal to the magnetic field, wherein theelectric field radiator has a second capacitive reactance adding to thetotal capacitive reactance, wherein a physical arrangement between theelectric field radiator and the magnetic loop results in a thirdcapacitive reactance adding to the total capacitive reactance, andwherein the total inductive reactance substantially matches the totalcapacitive reactance.

In the embodiment, the electric field radiator and the radiator feed maybe positioned inside of the magnetic loop or may be outside of themagnetic loop.

In the embodiment, the first electrical trace may couple to the magneticloop at a connection point, the connection point including an electricaldegree location approximately 90 degrees or approximately 270 degreesfrom a drive point of the magnetic loop, or a reflective minimum pointwhere a current flowing through the magnetic loop is at a reflectiveminimum. In the embodiment, the second electrical trace may couple tothe magnetic loop at a connection point, the connection point includingan electrical degree location approximately 90 degrees or approximately270 degrees from a drive point of the magnetic loop, or a reflectiveminimum point where a current flowing through the magnetic loop is at areflective minimum.

In the embodiment, a first width of the first portion of the magneticloop may be greater than or less than a second width of a second portionof the magnetic loop. In the embodiment, adjusting a position of thecapacitive gap may tune an impedance of the antenna.

FIGS. 12, 13 and 14 illustrate a front view, a back view and aperspective view, respectively, of an embodiment a multiband antennawith a capacitively coupled magnetic loop. This embodiment operates inthe 2.4/5.8 GHz bands and is approximately 0.217 by 0.35 inches inphysical size, further illustrating the compact size of the antennasdescribed herein. Farfield patterns for this embodiment at 2.4 GHzindicate that the pattern is omnidirectional, much like a dipolepattern. An E-field plot for this embodiment at 2.4 GHz indicates that afirst non-CPL e-field is generated by the loop and a second CPL e-fieldis generated by a combination of the radiator and the loop, asapproximately indicated by the dotted line 32. In particular themagnetic loop can be thought of as being separated by the capacitive gapinto an upstream portion and a downstream portion. The upstream portioncapacitively feeds the downstream portion of the magnetic loop. Theupstream portion of the loop emits the first e-field at a firstfrequency band. The electric field radiator, which is coupled to themagnetic loop via an electrical trace, in combination with a portion ofthe upstream portion and a portion the downstream portion emit a secondelectric field that is orthogonal to the magnetic field at a secondfrequency band. Hence, the electric field radiator resonates in phasewith the upstream portion and the downstream portion of the magneticloop at the second frequency band. In addition, as with such CPLantennas, the total inductive reactance of the antenna substantiallymatches the total capacitive reactance of the antenna.

In the embodiment of FIGS. 12-14, the capacitive gap 34 is approximately0.018 inches. The smaller this dimension, the lower the frequency of theloop. The capacitive gap 34 cannot become too large (too far apart), orthe capacitive coupling may begin to fail and the resonance maydisappear. The vertical position of the capacitive gap affects theimpedance matching of the antenna, hence moving the position of the gapup or down can be used to tune the antenna. The radiator 36 can also beused to tune the antenna. The skinnier component 38 of the magnetic loopis formed thinner for inductive reactance and to match the capacitivereactance of the capacitive gap 34. The length of the magnetic loop andthe first leg 40 of the magnetic loop act as a monopole for the secondresonance as illustrated in the return loss chart of FIG. 16, whichshows return loss minimized at approximately at 2.4 GHz and 5.8 GHz.FIG. 15 illustrates the feed point 42 and ground connection 44 of theembodiment when connected to a load.

FIGS. 17, 18 and 19 illustrate a front view, a back view and aperspective view (from the front), respectively, of an embodiment of amultiband CPL antenna with a capacitively coupled magnetic loop and acut loop wire completing the loop. This embodiment operates in the samemanner as the embodiment of FIGS. 12-15 and operates in the 2.4/5.8 GHzbands. This embodiment is, however, approximately 0.195 by 0.359 inchesin physical size, further illustrating the compact size of the CPLantennas described herein. As illustrated in FIG. 19, the feed point 50and ground connection 52 may be connected to a load (not shown). Thecapacitive gap 54 may be approximately 0.018 inches, the radiator 56,and the skinny matching element 58. The loop length and the first leg 60of the loop may act as a monopole for the second resonance. The threedimensional (3D) wire 62 may be used to complete the loop whilemaintaining a smaller two dimensional (2D) space on the printed circuitboard (PCB) on which the antenna is situated. When space is at apremium, such as on the PCB of a smart phone or other mobile device, the0.022 inch difference between the embodiment of FIGS. 12-14 and theembodiment of FIGS. 17-19 may be significant. The return loss chart forthis embodiment is illustrated in FIG. 20, which shows return lossminimized at approximately at 2.4 GHz and 5.8 GHz.

FIGS. 21, 22 and 23 illustrate a front view, a back view and aperspective view, respectively, of an embodiment of a double-sidedmultiband CPL antenna with a capacitively coupled magnetic loop with theloop completed on a second layer. This embodiment operates in the samemanner as the prior two embodiments in the 2.4/5.8 GHz bands, but isapproximately 0.17 by 0.359 inches in physical size, making it slightlyskinnier than the embodiment illustrated in FIGS. 17-19. As illustratedin FIG. 25, the feed point 70 and ground connection 72 may be connectedto a load (not shown). The capacitive gap 74 may be approximately 0.022inches, the radiator 76, and the skinny matching element 78. The looplength and the first leg 80 of the loop may act as a monopole for thesecond resonance. The extension to the second layer 82 may be used tocomplete the loop while maintaining a smaller 2D space on the PCB onwhich the antenna is situated. The width and length of the extension 82may also be used to tune the antenna, and physical shape may bemeandered to add more inductance to the antenna, if needed. The returnloss chart for this embodiment is illustrated in FIG. 24, which showsreturn loss minimized at approximately at 2.4 GHz and 5.8 GHz.

In an embodiment a multi-band compound loop antenna may comprise: amagnetic loop at least partially located on a first plane and generatinga magnetic field, the magnetic loop including a downstream portion andan upstream portion, the downstream portion separated from the upstreamportion by a capacitive gap that capacitively feeds the downstreamportion of the magnetic loop, the upstream portion configured to emit afirst electric field at a first frequency band and orthogonal to themagnetic field, wherein the capacitive gap adds a first capacitivereactance to a total capacitive reactance of the antenna; and anelectric field radiator located on the first plane, the electric fieldradiator coupled to the magnetic loop via an electrical trace, whereinthe electric field radiator coupled with the upstream portion and thedownstream portion of the magnetic loop is configured to emit a secondelectric field orthogonal to the magnetic field at a second frequencyband, wherein the electric field radiator is configured to resonate inphase with the upstream portion and the downstream portion of themagnetic loop at the second frequency band, and wherein a totalinductive reactance of the antenna substantially matches the totalcapacitive reactance of the antenna.

In the embodiment, the electric field radiator may be positioned insideof the magnetic loop. In the embodiment, the electrical trace may coupleto the magnetic loop at a connection point, the connection pointincluding an electrical degree location approximately 90 degrees orapproximately 270 degrees from a drive point of the magnetic loop, or areflective minimum point where a current flowing through the magneticloop is at a reflective minimum. In the embodiment, a first width of afirst portion the downstream portion of the magnetic loop is greaterthan or less than a second width of a second portion of the downstreamportion of the magnetic loop.

In the embodiment, the capacitive gap may add a capacitive reactance toa total capacitive reactance of the antenna, and adjusting a position ofthe capacitive gap may tune an impedance of the antenna.

In the embodiment, the downstream portion may be separated into a firstpart on the first plane and a second part on the first plane and includea three dimensional wire extending away from the first plane thatcouples the first part to the second part, or a third part on a secondplane that couples the first part to the second part. In the embodiment,a width and a length of the third part may be used to tune the antennaand a physical shape of the third part may be used to add inductance tototal inductive reactance of the antenna.

While the present disclosure illustrates and describes severalembodiments, it is to be understood that the techniques described hereincan have a multitude of additional uses and applications. Accordingly,the invention should not be limited to just the particular descriptionand various drawing figures contained in this specification that merelyillustrate various embodiments and application of the principles of suchembodiments.

What is claimed:
 1. A compound loop antenna, comprising: a magnetic looplocated on a first plane and generating a magnetic field, the magneticloop including a downstream portion and an upstream portion, thedownstream portion separated from the upstream portion by a capacitivegap that capacitively feeds the downstream portion of the magnetic loop,wherein the capacitive gap adds a first capacitive reactance to a totalcapacitive reactance of the antenna; and an electric field radiatorlocated on the first plane, the electric field radiator coupled to themagnetic loop and configured to emit an electric field orthogonal to themagnetic field, wherein a total inductive reactance of the antennasubstantially matches the total capacitive reactance.
 2. The antenna asrecited in claim 1, further comprising a radiator feed coupled to themagnetic loop, wherein the electric field radiator is positionedadjacent to the radiator feed, wherein the electric field radiator isseparated from the radiator feed by a second capacitive gap thatcapacitively feeds the electric field radiator, wherein the secondcapacitive gap has a second capacitive reactance adding to the totalcapacitive reactance.
 3. The antenna as recited in claim 2, furthercomprising an electrical trace coupling the radiator feed to themagnetic loop.
 4. The antenna as recited in claim 3, wherein theelectrical trace couples the radiator feed to the magnetic loop at aconnection point, the connection point including an electrical degreelocation approximately 90 degrees or approximately 270 degrees from adrive point of the magnetic loop, or a reflective minimum point where acurrent flowing through the magnetic loop is at a reflective minimum. 5.The antenna as recited in claim 3, wherein the radiator feed is directlycoupled to the magnetic loop.
 6. The antenna as recited in claim 1,further comprising an electrical trace coupling the electric fieldradiator to the magnetic loop.
 7. The antenna as recited in claim 6,wherein the electrical trace couples the electric field radiator to themagnetic loop at a connection point, the connection point including anelectrical degree location approximately 90 degrees or approximately 270degrees from a drive point of the magnetic loop, or a reflective minimumpoint where a current flowing through the magnetic loop is at areflective minimum.
 8. The antenna as recited in claim 6, wherein theelectrical trace is positioned on a second plane below the first plane9. The antenna as recited in claim 1, wherein the electric fieldradiator is directly coupled to the magnetic loop at a connection point,the connection point including an electrical degree locationapproximately 90 degrees or approximately 270 degrees from a drive pointof the magnetic loop, and a reflective minimum point where a currentflowing through the magnetic loop is at a reflective minimum.
 10. Theantenna as recited in claim 1, wherein a first width of a first portionof the magnetic loop is greater than or less than a second width of asecond portion of the magnetic loop.
 11. The antenna as recited in claim1, wherein adjusting a position of the capacitive gap along the magneticloop tunes an impedance of the antenna.
 12. A multi-band compound loopantenna, comprising: a magnetic loop located on a first plane andgenerating a magnetic field, wherein a first portion of the magneticloop is configured to emit a first electric field orthogonal to themagnetic field at a first frequency band; a radiator feed located on thefirst plane and coupled to the magnetic loop via a first electricaltrace, wherein the radiator feed is configured to resonate in phase withthe first portion of the magnetic loop at the first frequency band; andan electric field radiator located on the first plane, the electricfield radiator coupled to the magnetic loop via a second electricaltrace positioned on a second plane below the first plane, the electricfield radiator positioned adjacent to the radiator feed and separatedfrom the radiator feed by a capacitive gap, wherein the electric fieldradiator is configured to emit a second electric field at a secondfrequency band and orthogonal to the magnetic field, and wherein a totalinductive reactance of the antenna substantially matches a totalcapacitive reactance of the antenna.
 13. The antenna as recited in claim12, wherein the electric field radiator and the radiator feed arepositioned inside of the magnetic loop.
 14. The antenna as recited inclaim 12, wherein the electric field radiator and the radiator feed arepositioned outside of the magnetic loop.
 15. The antenna as recited inclaim 12, wherein the first electrical trace couples to the magneticloop at a connection point, the connection point including an electricaldegree location approximately 90 degrees or approximately 270 degreesfrom a drive point of the magnetic loop, or a reflective minimum pointwhere a current flowing through the magnetic loop is at a reflectiveminimum.
 16. The antenna as recited in claim 12, wherein the secondelectrical trace couples to the magnetic loop at a connection point, theconnection point including an electrical degree location approximately90 degrees or approximately 270 degrees from a drive point of themagnetic loop, or a reflective minimum point where a current flowingthrough the magnetic loop is at a reflective minimum.
 17. The antenna asrecited in claim 12, wherein a first width of the first portion of themagnetic loop is greater than or less than a second width of a secondportion of the magnetic loop.
 18. The antenna as recited in claim 12,wherein the capacitive gap adds a capacitive reactance to the totalcapacitive reactance of the antenna, and wherein adjusting a position ofthe capacitive gap tunes an impedance of the antenna.
 19. A multi-bandantenna, comprising: a magnetic loop at least partially located on afirst plane and generating a magnetic field, the magnetic loop includinga downstream portion and an upstream portion, the downstream portionseparated from the upstream portion by a capacitive gap thatcapacitively feeds the downstream portion of the magnetic loop, theupstream portion configured to emit a first electric field at a firstfrequency band, wherein the capacitive gap adds a first capacitivereactance to a total capacitive reactance of the antenna; and anelectric field radiator located on the first plane, the electric fieldradiator coupled to the magnetic loop via an electrical trace, whereinthe electric field radiator coupled with the upstream portion and thedownstream portion of the magnetic loop is configured to emit a secondelectric field orthogonal to the magnetic field at a second frequencyband, wherein the electric field radiator is configured to resonate inphase with the upstream portion and the downstream portion of themagnetic loop at the second frequency band, and wherein a totalinductive reactance of the antenna substantially matches the totalcapacitive reactance of the antenna.
 20. The antenna as recited in claim19, wherein the electric field radiator is positioned inside of themagnetic loop.
 21. The antenna as recited in claim 19, wherein theelectrical trace couples to the magnetic loop at a connection point, theconnection point including an electrical degree location approximately90 degrees or approximately 270 degrees from a drive point of themagnetic loop, or a reflective minimum point where a current flowingthrough the magnetic loop is at a reflective minimum.
 22. The antenna asrecited in claim 19, wherein a first width of a first portion thedownstream portion of the magnetic loop is greater than or less than asecond width of a second portion of the downstream portion of themagnetic loop.
 23. The antenna as recited in claim 19, wherein thecapacitive gap adds a capacitive reactance to a total capacitivereactance of the antenna, and wherein adjusting a position of thecapacitive gap tunes an impedance of the antenna.
 24. The antenna asrecited in claim 19, wherein the downstream portion is separated into afirst part on the first plane and a second part on the first plane andincludes a three dimensional wire extending away from the first planethat couples the first part to the second part.
 25. The antenna asrecited in claim 19, wherein the downstream portion is separated into afirst part on the first plane, a second part on the first plane and athird part on a second plane that couples the first part to the secondpart.
 26. The antenna as recited in claim 25, wherein a width and alength of the third part is used to tune the antenna.
 27. The antenna asrecited in claim 25, wherein a physical shape of the third part is usedto add inductance to total inductive reactance of the antenna.